Energy harvesting is the practice of capturing energy, converting or rectifying it into usable electrical power, for example DC (direct current power), and storing or using the converted electrical power. There are many sources of ambient energy in urban environments that can be harvested. These sources of energy include, but are not limited to, heat and electromagnetic energy.
The concept of rectification of microwave signals to DC power is known. Conventionally, high power microwave energy has been beamed to power airplanes, helicopters and even satellites. In order to convert electromagnetic energy into usable DC power, the received signals that create an induced AC (alternating current) in an antenna must be rectified to produce the DC power.
RF (Radio Frequency) energy is widely available for harvesting. RF energy, such as that used in Wi-Fi, TV signals, Wi-Max and cellular networks is scattered in all directions and available at various frequencies. Thus, recent work has focused on the design of rectennas (antennas attached to rectifiers) specifically for RF harvesting purposes. For example, as shown in the conventional RF energy harvester 200 of FIG. 1, a receiving antenna 203 capable of collecting electromagnetic (EM) energy within the frequency band of 700 MHz to 3 GHz is attached to rectifier 205. The receiving antenna 203 receives incident EM wave 201 comprising, for example, RF energy which induces an AC response in the antenna. The rectifier 205 rectifies the AC current into DC current which can then be transferred to a storage device 207, such as a battery, which is attached to rectifier 205.
Solar energy is a high energy source that can be converted by a photovoltaic (PV) device into electrical energy and used for charging batteries, for example, lithium-ion or other types of batteries of mobile devices that include solar integrated chargers. However, in some environments, such use can be limited by the availability of a light emitter, such as the sun.
Heat can also be harvested by capturing ambient heat, such as heat from stoves and heaters. Various machines and electronics also emit heat that can be harvested by, for example, a thermophotovoltaic (TPV) device, such as a Low-temperature thermophotovoltaic (LT-TPV) device.
Conventional energy harvesters are limited by the shortcomings of their designs, such as being limited to capture from only one source of energy. They are also limited by their inability to optimize the capture of energy emanating from different directions, different sources and at different times. Additionally, conventional energy harvesters are limited by variables of a particular environment, such as the energy density of a particular kind of energy. What is needed in the art, therefore, is a multifunctional and reconfigurable energy harvester that can achieve higher efficiencies than conventional energy harvesters.